1. Field of the Invention
The present invention relates to a multifibrous carbon fiber and its utilization, and, particularly to a multifibrous carbon fiber having the characteristics, such as excellent hydrogen adsorbing ability and oil adsorbing ability. The present invention also relates to a hydrogen adsorbing or hydrogen storage material, a hydrogen adsorbing method and a hydrogen adsorbing carbon.
2. Background of the Invention
Expanded graphite using natural graphite materials as starting material has been known. However, it has the problem of difficult processability.
Also, a fabrication method in which expanded graphite is compression-molded and a binder is added is proposed in the publication of JP 5-96157A. However, the method in which a binder is added is troublesome.
In the meantime, activated carbon and nanomaterial carbon materials such as a carbon nanotube and carbon nanofiber have been known as carbon materials for hydrogen adsorption. Activated carbon is a relatively inexpensive material and is used for a variety of adsorbents in industrial fields. However, activated carbon has small hydrogen adsorbing capacity as the hydrogen adsorbent and therefore has an insufficient performance. Also, the nanomaterial carbon materials such as a carbon nanotube and carbon nanofiber have relatively high hydrogen adsorbing capacity and are hydrogen adsorbents which are expected to be put to practical use. These carbon materials are increased in production and refining costs and therefore have an economical difficulty in utilizing these materials.
As a method of producing the nanomaterial carbon materials, a method of the production of a carbon nanotube and carbon fibril as disclosed in JP 3-174018A, JP 3-64606B and Japanese Patent No. 2982819 and methods of the production of carbon nanofibers as disclosed by Chambers et al., J. Phys. Chem. B, 122, 4253 (1998) and Fan et al., Carbon, 37, 1649 (1999) are known. However, all of these methods adopt a synthetic method by means of a vapor phase method using a metal fine powder as a catalyst, giving rise to the problem of uneasy mass production, troublesome works for the removal of the catalyst and high production costs.
With regard to recent carbon nanotubes, it is inferred and presumed that the carbon nanotube exhibits a highest adsorption density when the carbon nanotube has a diameter of 1.174 nm, namely an inside diameter of 0.7 nm as a calculated optimum size for hydrogen adsorption as reported by, for instance, Darkrim et al., J. Chem. Phys., 109, 4981 (1998) and Wang et al., J. Phy. Chem. B., 103, 4809 (1999). However, no concrete means has been found as to how to produce a carbon material having a pore size close to 0.7 nm and how to use this carbon material for hydrogen adsorption.
On the other hand, the layer distance of graphite is the order of 0.335 to 0.349 nm and therefore graphite cannot be an excellent hydrogen adsorbing body if it is used as a hydrogen adsorbent as it is.
In this respect, expanded graphite using a natural graphite material as starting material has been known as materials having a relatively large layer distance. This expanded graphite has the problem of difficult processability.
It is an object of the present invention to provide techniques which enables carbon fibers to have new structural characteristics exhibiting excellent hydrogen adsorbing characteristics and oil adsorbing characteristics.
Another object of the present invention is to provide a novel hydrogen adsorbing method, a hydrogen occluding agent, hydrogen adsorbing carbon and a hydrogen adsorbent.
Further objects will be apparent from the following descriptions.
The present invention is, in an aspect, a multifibrous carbon fiber obtained by processing carbon fiber including graphitized fiber electrochemically in an acidic solution for a time sufficient to run a layer reaction or intercalation reaction such that the reaction extends to the inside of the fiber.
The present invention is, in another aspect, the above carbon fiber, wherein heat treatment is performed at 200 to 1200xc2x0 C. after the electrochemical treatment to thereby expand the layer spacing.
The present invention is, in a further aspect, a hydrogen adsorbent comprising a carbon fiber layer reaction product which is obtained by processing carbon fiber electrochemically in an acidic solution and contains a carbon structure established such that the diffraction peak position (2xcex8) obtained by wide-angle x-ray diffraction analysis appears at 9 to 14 degrees.
The present invention is, in a further aspect, a hydrogen adsorbing method comprising bringing hydrogen into contact with the aforementioned hydrogen occluding agent and a hydrogen adsorbing carbon obtained by the method.
The present invention is, in a further aspect, a hydrogen adsorbing method comprising bringing hydrogen into contact with a carbon fiber layer reaction product which is obtained by processing carbon fiber electrochemically in an acidic solution and contains a carbon structure established such that the diffraction peak position (2xcex8) obtained by wide-angle x-ray diffraction analysis appears at 9 to 14 degrees.
The present invention is, in a further aspect, a method of adsorbing and desorbing hydrogen, the method comprising adsorbing hydrogen in the inside of multifibrous carbon fiber by bringing hydrogen into contact with a carbon fiber layer reaction product which is obtained by processing carbon fiber electrochemically in an acidic solution and contains a carbon structure established such that the diffraction peak position (2xcex8) obtained by wide-angle x-ray diffraction analysis appears at 9 to 14 degrees, to produce hydrogen adsorbed carbon and processing the hydrogen adsorbed carbon under heating and/or reduced pressure to thereby release the adsorbed hydrogen.
The present invention is, in a further aspect, a hydrogen adsorbing method comprising bringing hydrogen into contact with multifibrous carbon fiber produced by processing carbon fiber including graphitized fiber electrochemically in an acidic solution for a time sufficient to run a layer reaction such that the reaction extends to the inside of the fiber and thereafter heat-treating the carbon fiber rapidly at temperatures above 100xc2x0 C. to expand the layer spacing, to adsorb hydrogen in the inside of the multifibrous carbon fiber.
The present invention is, in a further aspect, the above hydrogen adsorbing method, wherein the multifibrous carbon fiber is carbon fiber having the characteristics that the specific surface area obtained by a nitrogen gas adsorption method is 50 to 500 m2/g and a broad diffraction line in which the peak position (2xcex8) obtained by wide-angle x-ray diffraction analysis is 20 to 25 degrees and the half-width of the diffraction is 1 to 5 degrees appears.
The present invention is, in a further aspect, a hydrogen adsorbing comprising multifibrous carbon fiber having the characteristics that the specific surface area obtained by a nitrogen gas adsorption method is 50 to 500 m2/g and a broad diffraction line in which the peak position (2xcex8) obtained by wide-angle x-ray diffraction analysis is 20 to 25 degrees and the half-width of the diffraction is 1 to 5 degrees appears.
The present invention is, in a further aspect, a hydrogen adsorbing carbon obtained by bringing hydrogen into contact with the aforementioned hydrogen adsorbent.
The present invention, in a further aspect, a method of adsorbing and desorbing hydrogen, the method comprising bringing hydrogen into contact with multifibrous carbon fiber produced by processing carbon fiber including graphitized fiber electrochemically in an acidic solution for a time sufficient to run a layer reaction such that the reaction extends to the inside of the fiber and thereafter heat-treating the carbon fiber rapidly at temperatures above 100xc2x0 C. to expand the layer spacing, to occlude hydrogen in the inside of the multifibrous carbon fiber, thereby forming hydrogen occluded carbon and processing the hydrogen occluded carbon under heating and/or reduced pressure to thereby desorb the adsorbed hydrogen.